DOC: small doc build warning: Note -> Notes
DOC: add demo of factorize
Merge pull request #5726 from jorisvandenbossche/patch-1

DOC: small doc build warning: Note -> Notes
Merge pull request #5731 from unutbu/factorize-doc

DOC: add demo of factorize
CLN: cache indexers in internal_names_set (reported GH5727)
BUG: Bug in multi-index selection in PY3 when using certain keys (GH5725)